In the course of progressive environmental legislation there is growing demand for sensors with whose aid even the minutest quantities of pollutants can be reliably determined. Above all, gas sensors that allow the determination of gaseous pollutants in the ppm range, independent of the temperature of the measuring gas, play an important role. However, especially the determination of the nitrogen oxide content in the combustion waste gases poses a special challenge because of the frequently high oxygen component in exhaust gases.
U.S. Application No. 2003/0075441 describes, for instance, a gas sensor which, among other things, is used to determine nitrogen oxides. Its method of functioning is assignable to what is known as the dual-chamber limit current principle. Measuring gas that enters the sensor is selectively rid of oxygen with the aid of two electrochemical pump cells situated one after the other in the flow direction of the measuring gas, and the partial pressure of the oxygen is therefore reduced considerably in this manner. The individual pump electrodes have different potentials, so that the oxygen content of the measuring gas can be reduced in a stepwise manner without changing the nitrogen oxide component in the measuring gas to any significant degree.
However, this sensor structure requires a multitude of electrical connections for contacting pump electrodes, measuring electrodes, heating elements etc. A high number of connections, however, leads to considerable expense with regard to routing the electrical feeds out of the sensor element, the electrical contacting and routing the cables out of the sensor housing. This results in high material and production expense and an increased quality risk.